feat: redesign track and master controls with integrated fader+meters+pan

Unified design language across all tracks and master section:
- Created TrackFader component: vertical fader with horizontal meter bars
- Created TrackControls: integrated pan + fader + mute in compact layout
- Created MasterFader: similar design but larger for master output
- Created MasterControls: master version with pan + fader + mute
- Updated Track component to use new TrackControls
- Updated PlaybackControls to use new MasterControls
- Removed old VerticalFader and separate meter components

New features:
- Horizontal peak/RMS meter bars behind fader (top=peak, bottom=RMS)
- Color-coded meters (green/yellow/red based on dB levels)
- dB scale labels and numeric readouts
- Integrated mute button in controls
- Consistent circular pan knobs
- Professional DAW-style channel strip appearance
- Master section includes clip indicator

Visual improvements:
- Unified design across all tracks and master
- Compact vertical layout saves space
- Real-time level monitoring integrated with volume control
- Smooth animations and transitions

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

components/editor/AudioEditor.tsx

@@ -35,6 +35,8 @@ export function AudioEditor() {
   const [selectedTrackId, setSelectedTrackId] = React.useState<string | null>(null);
   const [zoom, setZoom] = React.useState(1);
   const [masterVolume, setMasterVolume] = React.useState(0.8);
+  const [masterPan, setMasterPan] = React.useState(0);
+  const [isMasterMuted, setIsMasterMuted] = React.useState(false);
   const [clipboard, setClipboard] = React.useState<AudioBuffer | null>(null);
   const [recordingTrackId, setRecordingTrackId] = React.useState<string | null>(null);
   const [punchInEnabled, setPunchInEnabled] = React.useState(false);
@@ -1042,11 +1044,22 @@ export function AudioEditor() {
           currentTime={currentTime}
           duration={duration}
           volume={masterVolume}
+          pan={masterPan}
           onPlay={play}
           onPause={pause}
           onStop={stop}
           onSeek={seek}
           onVolumeChange={setMasterVolume}
+          onPanChange={setMasterPan}
+          onMuteToggle={() => {
+            if (isMasterMuted) {
+              setMasterVolume(0.8);
+              setIsMasterMuted(false);
+            } else {
+              setMasterVolume(0);
+              setIsMasterMuted(true);
+            }
+          }}
           currentTimeFormatted={formatDuration(currentTime)}
           durationFormatted={formatDuration(duration)}
           isRecording={recordingState.isRecording}